Kinetic mechanism and substrate specificity of nitroalkane oxidase

Nitroalkane oxidase from Fusarium oxysporum catalyzes the oxidation of nitroalkanes to aldehydes, transferring the electrons to oxygen to form hydrogen peroxide. The steady-state kinetic patterns have been determined with nitroethane, 1-nitropropane, and 1-nitropentane as substrates. In all three cases, the data fit best to a ping pong kinetic mechanism. The pH dependences of the V/K values for 1-nitropentane and phenylnitromethane show that an amino acid residue on the enzyme with a pKa-value of 6.7 must be unprotonated for activity with both substrates. A second group must be protonated for activity. The pKa value of this group matches the pKa values of the nitroalkanes, 9.3 with nitropropane and 6.7 with phenylnitromethane, establishing that the nitroalkane must be in the neutral rather than the anionic form for catalysis.